A window, whether it is a single- or double-pane, can get broken during a storm or from an errant baseball. The glass used in a double-pane window is insulated and has a barrier of air or inert gas between the two panes of glass. When the seal that surrounds the glass is broken moisture can get into the window and cause condensation. Replacing glass in a double-pane window will require taking the old glass out of the existing window panel.
Extract the window panel from the window. A sliding panel can be removed by pulling out on the bottom of the panel while lifting it up. A panel that is stationary can be removed by loosening the screws on the top and bottom of the panel with a screwdriver.
Remove the old glass pane from the frame. Take out the screws that hold the frame together with a screwdriver. Use a rubber mallet to tap on the frame to separate the glass pane from the frame.
See if there are any rubber stops within the frame. Set the stops aside if any are found, as they will be needed when the new glass pane is installed.
Place the rubber stops back into the frame and place it around the new glass pane. Insert the screws back into the frame and tighten them with the screwdriver.
Seal the frame by running a bead of caulk between the glass and the frame. This will prevent moisture from developing on the window as well as provide a cushion for the glass against the frame.
Insert the frame back in the window and replace any screws.
Put the frame on a table or saw horses before removing the glass pane.
Always wear heavy gloves in case the glass breaks. Regular window putty should not be used to seal the window.